JPS6316808B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to magnetic recording, and more particularly to a magnetic recording method and apparatus for recording information signals on a magnetic medium. In magnetic recording of information signals on magnetic media, such as magnetic tape, magnetic recording cores with large magnetoresistive gaps are commonly used. A magnetic flux corresponding to the signal to be recorded is generated in the recording core by suitable means and extends outwardly from the gap of the recording core as it bridges the gap. By suitably locating the recording core in contact with the medium, the magnetic flux of the striped magnetic field extending from the gap contacts and remains on the magnetic medium to record signal information on the medium. To reproduce the signal information recorded on this medium, a reproduction magnetic core with a gap is usually used. The playback core (which may in some cases be a recording core used for playback) collects the magnetic flux of the signal recorded on the medium in its gap; (assuming that there is relative motion between In signal reproduction, it is well known that in order to reproduce recorded short wavelength signals, the reproduction gap is made approximately half the length of the recording gap. Here, "wavelength" refers to
Refers to the distance along a recording on a recording medium between successive similarly magnetized portions of the medium. That is, the length of this playback gap defines the shortest signal wavelength that can be recovered during playback of a recorded signal. Although we think it appropriate to explain the definition of gap length here, the term "gap length" as used in this text refers to the length of the gap in relation to either recording or playback cores. It should not be taken to imply the physical distance between the magnetic poles of the core at either end; this physical distance is often referred to as "physical gap length,""optical gap length," or "mechanical gap length." ” is called. As used in this text, "gap length" means "magnetic gap length" unless otherwise specified. This magnetic gap length of the magnetic head is determined by (1) recording a set of test signals at various wavelengths on the magnetic medium using a suitable type of reference magnetic head, and (2) performing the test. (A they "magnetic tape recording")
(Discussed by NASA Publication No. SP-5038, page 66), the wavelength thus determined is equal to the magnetic gap length of the head under test. In support of the proposition that there is a difference between the magnetic gap length and the physical gap length, A. "It's longer than the average gap." It can be seen that in the tests described above, the recording head whose magnetic gap length is to be determined is used in a playback mode to play back the test signal. Just as it is well known to use optimal short playback gap lengths, it is also well known in the art to use relatively long recording gap lengths in practice. That is, the theory is that the trailing edge of the gap with respect to a recording medium in relative motion is the primary head associated with the recording process, and in such cases, the recording gap lengths should be compared. By increasing the magnetic field, the recording magnetic flux is spread outward from the recording gap to a large extent, thereby effectively recording the depth of the magnetic medium even in areas downstream of the recording gap. That has been explained. The recording gap length clearly affects the size of the recording area within the magnetic medium. That is, the shorter the recording gap length, the narrower the recording area for the same recording current. This is an important consideration because it is interrelated with separating short wavelength signals during reproduction. Indeed, if a narrow band of relatively short wavelength signals is to be recorded and reproduced, the recording gap can be relatively short. However, recording becomes difficult when long wavelength recording is involved, as in the case of broadband recorders. Regarding this point,
The paper “Physics of Magnetic Recording” by CDMee
(John Wiley and Sons, Inc. New York, 1964
It is discussed on page 245 of the annual publication). That is, ``...the recording area for a narrow gap recording head is shown......it can be seen that the narrowest recording area (1) is achieved, but only if a sufficient magnetic field is applied to completely magnetize the tape. Given this, this recording area is just as large as that from a wide gap head.Therefore, for broadband recording there is no benefit from using a gap that is too narrow.'' Similarly, A they mentioned above. In his work (page 23), he states the following: ``However, the operating gap in the read head is usually much smaller than in the record head.'' Others in the art have said this as well. For example, "Video Recording Recording and Playback Systems" by G. White (Grane, Russak and
Company, Inc. 1972) and “Magnetic Recording” by CELowman (Mc Graw-Hill Book Company,
(published in 1972). Suggested in the literature on broadband recording methods is the recognition that recorders such as quadruple helical scan video recorders can use the same relatively narrow gap head for recording and playback purposes. This is because these are relatively short wavelength/narrow band recorders. Indeed, as shown in the table below, all such recorders are for recording below a single octave. That is,

[Table] For broadband recording, for example in instrumentation recorders, or direct recording of audio and video information at relatively slow write speeds, it is practical to use wide gap heads for recording and playback. For use, use a head with a narrow gap. According to Lowman, p. 35, cited above, for example, a typical instrumentation recorder uses recording and playback gaps as described below. That is,

[Table] Also, if we calculate the shortest wavelength that can be recovered for each response of the above ABC, then the regeneration gap mentioned earlier is actually the physical gap length, and its upper limit for the magnetic gap length dimension. are 15.24μm (600μ″), 5.08μm (200μ″), and 1.52, respectively.
μm
(60 μ″). In contrast to general and specific teachings in the art, if magnetic recording is performed with a recording head having a recording magnetic gap length of less than about 0.38 μm, one octave Relatively large playback efficiencies are obtained for bandwidths larger than When recording on a magnetic medium consisting of magnetic particles with cubic and acicular anisotropy, the efficiency of the recording action improves itself, and the reproduction power-to-noise ratio (NP ratio) is desirably flattened. The present invention will now be described with reference to the accompanying drawings. The present invention can be easily implemented using the same head at surprisingly low head-to-tape playback speeds of about 0.1 cm/sec (0.04 in/sec). It was conceived in an attempt to provide high quality broadband acoustic recording on magnetic tape that could be both recorded and played back economically. It is no wonder that a recording head with a short gap is used to record, and given the availability of a playback head with a short gap, it is no wonder that very short wavelengths can be recovered. playback speed (approximately 0.127 mm (5 mil)
The unit area of the tape is 14.52 cm ² for the track width of
(results in 2 hours of playback per 1 1/2 square inch)
In order to make this possible, the read head must have a magnetic gap length of approximately 0.33 μm (13 μ″) or less, assuming a band of up to 3 KHz.
The art teaches that such a short playback gap length means that if the playback gap were also used as a recording gap, there would be very little striped magnetic field available for recording in the medium. It meant. It was therefore expected that it would be difficult to hope for progress. That is, it was expected that if no substantial recording took place on the medium, no appreciable playback could occur. However, contrary to expectations, if recording is performed with a recording magnetic gap length of about 0.38 μm (15 μ″) or less, effective reproduction is possible or even better. Next, the invention is first discussed in relation to the signal-to-noise (SN) ratio of the gap, distortion and channel capacity, and then the progressive use of micro-gap recording is discussed in Harband, P091EF, Hampshire, UK. , Homewell's Industrial Opportunities
Ltd., published in December 1977, available from
Research Disclosure, Vol. 164, No. 16476, described in conjunction with the generic media disclosed therein, further results of such a combination in terms of signal-to-noise and NP ratios were obtained. Next, using the conventional recording magnetic gap and the recording magnetic gap according to the present invention, respectively, the same recording medium (i.e., the above-mentioned "Research
Please refer to Figure 1, which shows a pair of curves showing the actual playback performance of recordings made on the media described in ``Disclosure''. For curve 1, DC
For recording frequency bands greater than 500KHz, the conventional physical gap length is approximately 1.93μm.
(76 .mu."), but regeneration was obtained using a regeneration magnetic gap length of approximately 0.3 .mu.m (12 .mu."). For curve 2, according to the present invention, approximately 0.3 μm
A magnetic gap length of (12 μ″) was used for both recording and playback purposes.
Although a loss of 6 dB occurred, when the present invention was implemented,
Not only does a gain of about 11 dB occur at the band edge corresponding to a wavelength of about 0.66 μm (26 μ″), but also the playback band edge according to the present invention can be extended to the point where the playback band edge also corresponds to a wavelength smaller than about 0.5 μm (20 μ″). expanded. Shannon's theorem ("Communication transmission systems", Bell
Telephone Laboratories, Inc. 1964, 610
According to (Page), if we keep in mind that the capacity C of a communication channel to transmit information without error is proportional to the channel's SN ratio and bandwidth W, that is, C = Wlog ₂ (1 + SN ratio), It is clear from the curves of FIG. 1 that the channel capacity of the microgap recording operation according to the invention is much better than that according to the conventional method. That is, in order to improve the overall SN ratio, the area under curve 2 must be larger than the area under curve 1, and since the recording effect of the small gap greatly expands the playback bandwidth, the channel capacity C must also become larger. Become. For a qualitative assessment of why microgap recording may still result in recording performance demonstrating superior reproduction signal-to-noise ratio, please now refer to the qualitative representation of FIG. In ideal recording at a certain wavelength λ, a defined recording area occurs on the medium (tape). Area 1
is completely magnetized to the positive polarity, region 2 is exclusively magnetized to the negative polarity, region 3 to the positive polarity, and region 4 to the negative polarity...
...and so on. However, in each region the magnetization strength changes from minimum to maximum and back to minimum. Thus, for such an ideal recording, if it is possible to move the read head with an undefined small read gap along and into contact with the record head, the magnetic flux will be The head gap is proportional to the intensity, thereby producing an undistorted reproduced signal with wavelength λ. However, under such conditions, magnetic recording of a signal having a wavelength λ does not occur as ideally shown. Rather, as the recording head moves relative to the recording medium, an arcuate recording area is created on the medium. The recording characteristics labeled "wide gap recording" in FIG. 2 represent typical state-of-the-art recording characteristics for signals having wavelength λ. What should be noted is that the recordings in areas 2, 3, 4, etc. overlap with the recordings in area 1, and as a result, when trying to play back the recordings in area 1, the following two problems will adversely affect the playback. give. That is, one of them is even numbered areas 2 and 4.
The magnetic flux of ...... reduces the distinguishable composite magnetic flux during reproduction, thereby lowering the initial reproduction S/N ratio. Second, as a result of the reduction of the composite reproduction magnetic flux caused by the even numbered regions 2, 4, etc., the reproduction magnetic flux is not linearly related to the recorded signal, and this causes distortion during signal reproduction. arise. According to the implementation of the present invention, overlapping of adjacent recording areas is suppressed to a minimum, and in this regard, please refer to the recording characteristic called "microgap recording" shown in FIG. 2. Since there is much less overlapping of the recorded areas, the reduction (and distortion) state of the reproducing magnetic flux is minimized, thus resulting in a reproducing characteristic as shown in curve 2 of FIG. As is well known, in prior art magnetic recording, the actual recording action that occurs on a medium moving relative to a recording gap occurs at a point in the medium downstream of the recording gap, and the strength of the magnetic field that causes magnetization at this point increases. is approximated by the coercive force of the medium. However, in recording a small gap, the point at which the actual recording action occurs substantially extends over the recording gap itself.
Such a recording action has the advantageous effect of reducing the phase difference between simultaneously recorded signals, thus reducing and simplifying the electronic elements required to perform phase equalization of the recorded signals. bring about. In other words, microgap recording reduces the vertical magnetization of the tape, which cannot be equalized simultaneously with the desired longitudinal magnetization. When performing microgap recording in conjunction with the recording medium characteristics of the recording medium disclosed in the above-mentioned "Research Diselosure," further improvements in playback performance can be achieved. Curve A in Figure 3
is a commercially available recording tape, namely Ampex.
Microgap recordings (0.3μ
The actual playback characteristics of a recording gap of m≒12 μ'' are shown.As is known, the particles constituting the Ampex Type 797 tape have shape anisotropy.In contrast,
The medium as disclosed in Research Disclosure consists of particles with acicular and cubic anisotropy. The magnetic recording flux in such media is most effective in creating remanence along the geometric axis of the magnetizable particles forming the media, although it is also effective along orthogonal axes. In this way, the efficiency during the recording operation is relatively improved.
When recorded with a small gap using the same head used to obtain the response of curve A in FIG. shows. What should be noted here again is approximately 0.66μm
The signal-to-noise ratio of reproduction is improved at signal frequencies corresponding to wavelengths of (26 μ″), but also for very long wavelengths and very short 0.45μm≒18μ″)
The point is that the reproduction SN ratio is improved for both wavelengths. For convenience, curve 1 of FIG. 1 is shown again in FIG. 3, which shows that while small gap recording provides an improvement regardless of the recording medium, an even larger and more dramatic improvement in playback performance occurs when the recording medium It can be seen that this can be achieved by making appropriate choices. Next, with respect to the NP ratio, such as the ratio of the power of recorded white noise to zero signal noise at a predetermined slot across the spectrum, slot noise arises from intermodulation caused by the recording medium itself. Ideally, there should be no such slot noise and the NP ratio should be as large as possible. Furthermore, the NP ratio should be as flat as possible with respect to frequency, since the entire bandwidth can be used most effectively. By pre-emphasizing the high-frequency components of frequencies in a certain bandwidth to be recorded, and de-emphasizing the high-frequency components during playback, the SN at such frequencies is reduced.
Bearing in mind that it is desirable to improve the ratio, reference should be made to the qualitative representations of FIGS. 4a and 4b. Curve A in FIG. 4a is a playback performance curve for small gap recording performed on media such as that disclosed in Research Disclosure, supra, at constant current and variable frequency. As mentioned above,
High frequency components are pre-emphasized (dotted line associated with curve A) prior to their recording, so that during their playback these frequency components are de-emphasized to improve the short wavelength signal-to-noise ratio. Curve B1 shows the playback noise (head noise, electronic noise, media noise) associated with small gap recordings made under zero signal and bias conditions. Curve B2 represents playback noise (head noise, electronic noise and media noise) associated with small gap recording.
shows the noise caused by the pre-emphasized zero signal and bias conditions. Also, curve B3
shows the playback noise (head noise, electronic noise, media noise) associated with the pre-emphasized white noise microgap recording as described above. It should be noted that the result of the intermodulation caused by recording such a white noise signal is to increase the noise level from that shown in curve B2 to that shown in curve B3. Due to the medium's ability to limit the production of intermodulation results by remaining relatively linear over a wide range of input levels, as disclosed in Research Disclosure, high-frequency pre-emphasis may Provides a high effective level of NP ratio. See curve C. On the other hand, curve A' in FIG. 4b shows the reproduction performance of state-of-the-art recordings at constant current and variable frequency. The recording head used here has a relatively wide gap, and the media is one of several commercially available types. Curve A′ (dashed line, curve
If it is desirable to pre-emphasize the high frequency components associated with A noise component is generated throughout the entire area. Curve B1' shows the playback noise (head noise, electronic noise, media noise) associated with state of the art recordings at zero signal and bias conditions. curve B
2' shows the playback noise associated with state-of-the-art recordings made with a pre-emphasized zero signal and bias conditions. Curve B3' shows the playback noise (head noise, electronic noise, media noise) associated with the pre-emphasized white noise input signal as described above. Although pre-emphasis on the high-frequency components associated with curve A' improves the signal-to-noise ratio at the band edge of short wavelengths, this pre-emphasis undesirably significantly impairs the level and flatness of the NP ratio, as shown in curve C'. become. Thus, it will be seen that the cooperative action between the media and the microgap recording head as disclosed in Research Disclosure, supra, provides numerous benefits from such action. With the aforementioned advantages in recording microgaps in mind, reference is made to FIGS. 5-7 which show various embodiments demonstrating the versatility of the recording device according to the invention. In all such embodiments, the same head is used for recording and playback, although a separate read head with a playback gap equal to or smaller than the record head can be used. Further, in order to carry out the present invention in its best mode, the recording medium used in such a magnetic recording apparatus is that disclosed in "Research Disclosure". Figure 5 shows that the tape is moving at the conventional speed (2.89 cm/sec≒
1 7/8 inch/sec), and because of the minute gap recording (recording gap: 0.3 μm≒12 μ″), the 1.42 μm
(56μ″) to 0.71μm (28μ″) recording wavelength/deviation value (carrier wavelength: 0.97μm≒38μ″), and such reproduction is possible from DC after demodulation.
A narrow band FM recorder is shown that extends to 12 KHz and provides a remarkable acoustic response of 60 dB at the upper band end of the acoustic spectrum. The device disclosed in FIG. 5 is for processing a spectrum slightly wider than one octave (although it is possible to process a spectrum less than one octave at the cost of performance), whereas the device shown in FIG. Approximately five full octaves of acoustic frequency, with recording/playback speeds of only 0.1 cm/s (0.04 inches/s)
That is, it is for direct recording and reproduction of frequencies from 100 to 3000 Hz. The wavelength recorded at such a speed varies in the range of 1.22 μm (48 μ″) to 0.36 μm (14 μ″), and the playback signal-to-noise ratio is quite good at 30 dB. FIG. 7 shows an instrumentation recorder for processing five octaves of data. Conventional instrumentation recorders have recording heads with wide gaps (typical example, physical gap length: 12.7 μm≒
500μ″) and a separate narrow gap regeneration head;
Good playback from 200 KHz to 1.2 MHz using a tape speed of 3.05 m/sec (120 in/sec). In accordance with the present invention, a multi-channel magnetic head with multiple 0.3 µm (12 µ'') magnetic gap lengths, each core used for both recording and reproducing purposes, allows only half the recording speed to be reduced to 1.52 m/s (60 in/s). ) can be used to perform good reproduction of wavelengths corresponding to frequencies from 200 KHz to 3.2 MHz. Of course, the writing speed can be achieved by moving the head in question relative to the recording medium, as is done, for example, in a quadruple helical scan recorder. However, microgap recording is not limited to recorders in which the medium moves relative to the head. The aforementioned apparatus can be used industrially to record information signals on magnetic media. The device can be used industrially as a recorder for recording audio signals and video information signals on magnetic tape.

[Brief explanation of the drawing]

Figure 1 is a graph showing a pair of curves illustrating the advantages of micro-gap recording, a recording method accomplished by the use of conventional recording gaps; Figure 2 is useful in explaining the theory of how micro-gap recording works. FIG. 3 is a graph showing a pair of curves illustrating the advantages of microgap recording in conjunction with a desirable recording medium; FIGS. 4a and 4b are graphs showing the improved NP ratio performance obtained from microgap recording. Graphs for explaining and Figures 5 to 7
The figure shows a recorder that is made possible by using the microgap recording method.

Claims (1)

[Claims] 1. A method for recording information signals on a magnetic medium using a magnetic recording head, comprising: (a) a recording magnetic head having a recording magnetic gap length of less than about 0.38 μm; (b) applying an information signal to the recording magnetic head for recording a signal on the magnetic medium. 2. The method of claim 1, wherein the magnetic medium comprises magnetic particles having both cubic anisotropy and acicular anisotropy. 3. A magnetic head provided with a gap for recording an information signal on a magnetic medium, a device for imparting relative motion between the head and the magnetic medium, and a magnetic head for recording the information signal on the magnetic medium. a device for providing information signals to
A magnetic recording device characterized by having a smaller recording magnetic gap length.